1. Field of the Invention
The present invention relates to polyolefins, and particularly to a method of promoting olefin polymerization that uses a nanoparticle filler to increase the activity of a metallocene catalyst for in situ polymerization of polyolefins. The filler may be nanoparticles of manganese, or nanoparticles of manganese-doped titanium dioxide.
2. Description of the Related Art
Polyolefins are by far the most common commercial polymers that we encounter in day-to-day life. A number of disadvantages prevent their wider use. Polyethylene is a polymeric material having the largest tonnage in the world with respect to production. Polyethylene possesses valuable properties in addition to its low cost, such as the ability to be recycled, good processability, non-toxicity and biocompatibility. However, due to the inherent chemical nature, both its stiffness and low temperature toughness are not satisfactory. Polymer nanocomposites are a unique new class of materials with an ultrafine dispersion of nanomaterials in a polymeric matrix. They show unique properties by combining the advantages of the inorganic nanofillers (e.g., rigidity, thermal stability) and the organic polymers (e.g., flexibility, dielectric, ductility, and processability). Such inorganic nanoparticles as silicon dioxide (SiO2), titanium dioxide (TiO2), aluminum trioxide (Al2O3), and zinc dioxide (ZrO2) have been used to improve polymer properties.
A variety of techniques have been used to incorporate such nanosize metal oxide fillers into polymers. For example, the nanoparticles may be mechanically mixed with the polymer resin and blended as a melt in extrusion, injection molding, or other plastics manufacturing processes. However, the melt blending technique does have a major disadvantage, since host-guest incompatibilities usually result in nanoparticle aggregation and phase separation, which is detrimental to the properties of the polymer composite. Solution mixing is another technique that has been used to prepare metal oxide-based polymer nanocomposites, but the process does not suit polyolefins, since the solubility of polyethylene, high-density polyethylene (HDPE), and polypropylene is too low in most low boiling organic solvents. Another problem is the hydrophilic nature of most inorganic fillers and the hydrophobic nature of the polyolefins, which results in weak interfacial adhesion between the filler and the polymer matrix, and in poor mechanical properties.
Thus, a method of promoting olefin polymerization solving the aforementioned problems is desired.